The present invention relates to a method and an apparatus for controlling an auxiliary motor, especially the present invention relates to a method and an apparatus for regulating voltage, current and frequency applied to an auxiliary motor.
During transportation of goods that have to be kept cold or frozen, vehicles provided with a cooling system are often utilized. The cargo is kept in a cargo space, which suitably is isolated, and a cooling system is arranged to cool the cargo space down to a given temperature that may be both above and below the freezing point. A cooling system comprises among other things a compressor, a coolant and a hose arrangement to convey the coolant.
In a vehicle with a cooling system as described above, the cooling system must in some way be operated with aid of the vehicle""s driving motor when the vehicle is transporting the goods. Then, when the vehicle is stationary and the driving motor is not running this way of operation is no longer available. When the vehicle is stationary the goods may be loaded to a cooling keep. Alternatively, the cargo space in the vehicle may be utilized by connecting the cooling system of the truck and operating it by an electric compressor mounted in the vehicle, which electric compressor for instance is connected to the regular power mains.
When the vehicle is driven the regular power mains may of course not be utilized in operation of the cooling system. Different alternatives then exist according to prior art. The most common way is to arrange a compressor in the engine bay, which is operated through a belt arrangement from the engine. Hose running must then be made from the cooling unit, which commonly is mounted on the roof of the vehicle, to and from the compressor in the vehicle""s engine bay. These hose running are of course a source of problem and results in among other things that service of the vehicle is made more expensive since only certified service shops may handle the coolant. Further, the use of two compressors entails extra costs.
The above-described solution according to the prior art suffers from the problem that the effect of the compressor is related to the number of revolutions of the driving motor. When the number of revolutions of the driving motor decreases the power of the compressor also decreases. The compressor and the cooling system must therefore be designed to be able to deliver the cooling necessary at the number of revolutions of the engine that is valid during idle running, or during some average number of revolutions valid during the traffic conditions that the cooling truck will be in, e.g. city traffic. This results in that the cooling system will be designed to have overcapacity. This in turn entails that the compressor, hoses and other material will be expensive.
According to JP 2001050630, Tsuboi Tokushu Shatai K K, xe2x80x9cDrive mechanism for refrigerating machine mounted on refrigerator carxe2x80x9d current is generated by means of a generator connected to the engine via a battery. The apparatus solves the problem to provide a constant power independent of the number of revolutions of the engine. However, the apparatus working order is limited by the capacity of the batteries and to obtain a greater power supply or power supply during a longer time there is probably necessary with relatively large batteries.
It is thus desirable to discover a way of reducing or completely avoiding the above-mentioned problems.
In a motor operating a load, preferably a compressor, it may be assumed, somewhat simplified, that the applied voltage and frequency specify the number of revolutions of the motor and the applied current specifies the torque the motor may yield.
The main purpose of the present invention is thus to provide an apparatus and a method for regulating current, voltage and frequency to a load, preferably a motor to provide an effective use of available power.
A specific purpose of the present invention is to provide an apparatus and a method that permit that a smaller cooling system may be utilized to obtain a given cooling capacity of a cooling system in a cooling vehicle.
Above mentioned purposes are provided by an apparatus and a method according to the enclosed independent claims.
Preferred alternatives and embodiments of the present invention are provided by apparatuses and methods according to the enclosed dependent claims.
An advantage of the present invention is that a cooling system in a cooling vehicle only needs one compressor arranged in connection with the cooling space of said cooling vehicle.
An advantage of the present invention is that the proportion of a corresponding cooling installation driven by a compressor arranged to be driven directly by a motor is reducible by a factor of 1.8 to 2.0. I.e. a cooling installation of 2.2 kW is exchangeable for a cooling installation of approximately 1.1 kW during favorable conditions.
Another advantage of present invention is that no hose running for conveying coolant is necessary from a compressor arranged at the engine of a cooling vehicle to a cooling installation arranged in connection with the cooling space in said cooling vehicle.
Another advantage of the present invention is that no battery function is necessary to be arranged in the cooling vehicle for the cooling system.
Another advantage is that a system solution is obtained where two compressors are exchanged for one, which saves weight and which in turn permits that the payload may be increased.
Further features of the invention and advantages thereof will be evident in the following detailed description of embodiments according to the invention.